1. Field of the Invention
The present invention relates to an ink-jet O/W emulsion ink, and an ink-jet recording method using the same.
2. Description of the Related Art
Conventionally, techniques for printing images, letters/characters, etc. onto recording paper by ink-jet method have been proposed.
Aqueous ink-jet inks have the merit of causing less bleeding and less strike-through, yielding high image densities, and so forth when printing is carried out using plain paper.
However, in the case where the aqueous ink-jet inks are attached onto recording paper in large amounts so as to print photographs, charts, etc. thereon, there is such a problem that the recording paper easily curls. When the recording paper curls, paper conveyance in ink-jet printers becomes troublesome; paper conveyance may possibly become difficult, especially at the time of high-speed printing or double-sided printing.
Because of the above-mentioned problem, a formulation of ink capable of reducing the occurrence of paper curling related to the amount of ink attached is hoped for.
As to high-speed ink-jet printers with line heads, in particular, there is a much greater need for the formulation of ink than in the case of serial printers. To reduce curling of recording paper, the following methods have been proposed, for example: a method of adding into an ink a copolymer of acrylic acid and vinylpyrrolidone having a molecular weight of approximately 80,000 to 250,000 (refer, for example, to Japanese Patent Application Laid-Open (JP-A) No. 10-1629); a method of adding into an ink a pigment and colloidal silica having an average particle diameter of 5 nm to 100 nm (refer, for example, to JP-A No. 09-227812); and a method of adding into an ink a water-soluble organic solvent whose solubility parameter is greater than or equal to 8 and less than 12 and a metal oxide colloid (refer, for example, to JP-A No. 2006-321876).
However, any of those conventionally proposed methods for reducing curling of recording paper is a method of reducing absorption of moisture in the ink into the recording paper, namely cellulose fiber, by adding a certain solid content into the ink. To reduce curling of the recording paper, it is necessary to maintain hydrogen bonds which act between cellulose molecules constituting the cellulose fiber; mere addition of a solid content into the ink allows an ink solvent (based upon alcohol, water, etc.) to permeate between the cellulose molecules, thereby causing the cellulose fiber to swell, and so cannot reduce the occurrence of curling of the recording paper.
Also, when an attempt is made to sufficiently reduce permeation of the ink solvent (based upon alcohol, water, etc.) between the cellulose molecules by adding a large amount of solid content into the ink, there is such a problem that the continuous ejection stability of the ink from an ink-jet head degrades, and the ejection stability of the ink from the ink-jet head degrades after left unused.